One strain of atypical rotavirus, morphologically indistinguishable from known rotaviruses but lacking the common group antigen of typical rotavirus detectable by an enzyme-linked immunosorbent assay (ELISA), was isolated from one of 152 Ecuadorian infants with acute rotavirus gastroenteritis. The genome analysis by polyacrylamide gel electrophoresis revealed a unique RNA pattern clearly distinct from that of typical rotaviruses.